Welding installations often involve multiple concurrent welding operations, with each welding operation being performed with one or more corresponding welding arcs. Typically, a welding power source is provided for each welding operation, where the power sources are each connected to AC input power supplies for providing welding arc power. These stand-alone welders include circuits with transformers and rectifiers to convert the supplied single or three-phase AC input power to a DC bus, typically around 50 to 120 volts DC, which is then applied to a control stage to create a signal suitable for establishing a welding arc. Many different forms of welder power sources have been developed, including inverter and chopper based designs that provide a welding signal waveform by selective switching of current from the DC bus. Examples of modern welding power source designs include POWERWAVE inverter-based products and POWERMIG chopper-based systems offered by the Lincoln Electric Company of Cleveland, Ohio. POWER MIG and POWER WAVE are registered trademarks of the assignee of the present invention. These welders provide control of the welder output waveform to enable advanced welding operations to control various parameters of a given welding application, where the waveforms can be designed using computer-based interface tools that communicate with a digital switching controller that operates the switching circuitry of the inverter or chopper stage following the initial AC-DC power conversion stage. Examples of these advanced welders and tools are shown in Blankenship U.S. Pat. No. 5,278,390; Hsu U.S. Pat. No. 6,002,104; Spear U.S. Pat. No. 6,486,439; Spear U.S. Pat. No. 6,624,388; Hsu U.S. Pat. No. 6,700,097; Hsu U.S. Pat. No. 6,717,108; and Hsu U.S. Pat. No. 6,734,394, which are incorporated by reference as background to the present invention. Advanced power sources commonly offer positive and negative outputs to support either polarity or variable polarity modules. The waveforms can be specified and saved in memory in the digital controller, and these welders can be configured to implement a wide range of welding operations. This advanced programmability has proved enormously successful in modern welding applications, allowing manufacturing and assembly processes to be optimized in a number of industries where workpieces are welded, and this technology has been widely offered in the market.
In many welding worksites, however, the power distribution may not be dispersed adequately to provide AC power at every location where a welder is required. In addition, the stand-alone welders are often heavy, typically well over 300 pounds, primarily due to the internal transformers and rectification components needed to convert the AC input power to a usable DC bus level from which a welding signal can be derived. Consequently, the welder (and hence the welding operation) must be located near a supply of AC electrical power, and an operator cannot easily relocate the welder. Distributed welding systems have been developed to operate multiple welding arcs from a large single AC-DC power source. In this manner, the AC supply is converted to a DC bus that is distributed by suitable cabling from the single AC-DC supply to a number of analog control modules that ultimately provide welding arc power to individual welding operations. In such distributed systems, the modules include a tapped resistor grid, with the output of each grid being adjusted by an operator to set the desired arc current (heat) for the corresponding welding process. In a common welding installation, the individual welding operations may require maximum arc current capabilities on the order of 300 amps or more, wherein the AC-DC supply typically provides a DC bus voltage of about 80 volts DC to the individual analog welding modules. Because several arcs may be simultaneously powered by the single AC-DC supply, the supply must be capable of maintaining adequate output voltage levels while supplying up to 1000 amps or more to the array of welding modules. In this regard, the resistive tap components make the individual modules energy inefficient, and the single AC-DC power source needs to be sized so as to provide the required welding currents with enough capacity to accommodate the module inefficiencies. As a result, higher levels of such system distribution require the AC-DC power source to be extremely large and heavy. Moreover, short circuit conditions in any one of the arcs provided by the analog control modules can cause loss of arc situations in other weld processes, due to the simple nature of the analog arc controls and the shared power source.
In early distributed welding systems, the efficiency and control capabilities of the individual weld modules were limited, due to the simple resistive tap arrangement, whereby advanced welding processes could not be undertaken in such prior distributed welding systems. To address the module inefficiency shortcomings, switching supplies have been developed for distributed welding systems, where a switching DC-DC converter module is used to provide the arc current in a multiple arc application. An example of this type of equipment is the Multi-Weld product line manufactured and sold by the Lincoln Electric Company of Cleveland, Ohio, with which any number of modules can be connected to a single DC power source to provide multiple welding arcs. The internal switching circuitry of these welding modules is conventionally controlled by dedicated analog control circuits configured for certain common welding operations, such as basic shielded metal arc welding (SMAW), gas-tungsten arc welding (GTAW), gas-metal arc welding (GMAW) or flux-cored arc welding (FCAW) processes. However, these systems do not offer the programmability and advanced control capabilities of the above mentioned waveform controlled stand-alone welders. Accordingly, there is a need for improved welding systems and apparatus by which advanced welding capabilities can be provided in welding situations where AC supply power is not widely distributed while allowing easy relocation and reconfiguration of equipment to different locations to perform different welding operations.